The present invention relates to a method for complete bainite hardening of steel for use in bearings and other load carrying components. The invention is useful in processing such steels as known to those in the relevant technical area.
Bainite hardening is sometimes preferred in steels instead of martensite hardening. This is because a bainitic structure in general has better mechanical properties, e.g., higher toughness, higher crack propagation resistance, etc. Therefore, for critical components such as bearings or other load carrying components especially subjected to fatigue, a bainitic structure could be most suitable.
Bainite hardening is widely used to produce components with high strength and hardness. For a given steel, the bainite structure often exhibits superior mechanical properties and structural stability compared to a martensite structure. The disadvantage with bainite hardening, however, is the long process time. To reduce the processing time for isothermal bainite transformation, it is necessary to increase the bainite transformation temperature. However, this will reduce the hardness which could affect the properties of the component.
GB, A, 2019436 discloses a method of producing a steel alloy which is tough, strong and economical. The method involves a bainite hardening treatment in the region of 0.degree. C. and 100.degree. C. above the martensite point, until a maximum transformation of 85%, preferably 80%, of the martensite to bainite. The steel is then cooled to room temperature. The method is more economical as there is a great savings in the time compared to a traditional complete transformation. However, the part of the steel which is not transformed into bainite does affect the properties of steel.